1. Field of the Invention
The present invention relates to a device for processing coded signals and a method of synchronizing coded signals. More particularly, the present invention relates to a coded signal processing device and a coded signal synchronizing method advantageously applicable to the processing of coded signals not synchronized to transmit or store the processed coded signals.
2. Description of the Background Art
It is a common practice to transmit a TV (television) or similar moving picture signal or store it in a desired recording medium by efficiently compressing it by use of an MPEG (Moving Picture Experts Group) or similar coding system. On the other hand, to combine two television signals not synchronized with each other or to switch from one to the other, it has been customary to synchronize them with, e.g., frame synchronizers and then combine or switch the resulting signals frame by frame or field by field. The frame synchronizers each separate a vertical and a horizontal synchronizing signal from the respective TV signal and write the TV signal in a buffer memory in accordance with the above two synchronizing signals. The TV signals are read out of the individual buffer memories in synchronization with each other in accordance with a vertical and a horizontal synchronizing signal derived from a reference synchronizing signal generated in local. The TV signals are then subjected to preselected processing.
A coded signal processing device of the type using the above frame synchronizers is conventional as a device for processing two different coded video signals and transmitting or storing the processed coded signals. This type of device, however, needs two decoders each for decoding a particular coded signal, e.g., an MPEG coded signal, two encoders for reproducing the original TV signals or composite signals from decoded component signals made up of a luminance signal (Y) and chrominance signals (C), the two frame synchronizers, a signal processor for executing combination, switching or similar signal processing, a decoder for converting the composite signals to component signals, and an encoder for again coding the component signals with a preselected coding system.
The two decoders each decode a particular coded signal input to the device and thereby output a digital component signal made up of a Y signal and C signals. The two encoders respectively transform the component signals output from the two decoders to composite signals on which the Y and C signals are superposed. The composite signals are converted to the original analog TV signals and then input to the frame synchronizers. At this instant, frame-by-frame or field-by-field horizontal and vertical synchronizing signals are separated from the TV signals and also input to the frame synchronizers.
Each frame synchronizer digitizes the TV signal input thereto and writes the resulting digital picture data in the respective buffer memory in accordance with a horizontal and a vertical synchronizing signal fed from the encoder. Such TV signals are read out of the buffer memories in accordance with a horizontal and a vertical synchronizing signal common to them and fed to the signal processor.
The signal processor combines the two synchronous video signals or switches them scene by scene to thereby output a single video signal. The video signal output from the signal processor is again converted to an analog signal and then transformed to Y and C component signals by the decoder. The encoder codes the component signals with, e.g., the MPEG coding scheme. The resulting coded signals are transmitted or written to a desired recording medium as efficiently compressed coded signals.
However, the problem with the conventional coded signal processing device must execute a sequence of steps of decoding coded video signals input thereto, converting the decoded signals to preselected signals , transforming the converted signals to analog signals, digitizing the resulting analog signals, and then processing the resulting digital signals, again transforming the processed digital signals to analog signals, again converting the analog signals to preselected signals, again digitizing the converted signals, and then coding the resulting digital signals. Image quality is deteriorated every time the signals are subjected to a signal conversion step.